textproduct: Rapid City

KEY MESSAGES

- Active pattern persists through mid-week with daily chances of storms, some of which may be strong to severe.

- Trending warmer to end the week into next weekend.

UPDATE

Issued at 1039 PM MDT Mon Aug 17 2026

No major changes made with this evening's forecast update. Adjusted PoPs and QPF to better match radar trends this evening, and broadbrushed PoPs a bit more across northeast Wyoming, the Black Hills, and southwestern South Dakota plains Tuesday afternoon based on the latest high-res guidance. A few storms Tuesday will once again be capable of producing damaging winds in excess of 60 MPH, hail, and very heavy rainfall.

DISCUSSION

(This Evening Through Monday) Issued at 1200 PM MDT Mon Aug 17 2026

Upper level analysis depicts near-zonal flow over the central US. Upper level moisture associated with a weak wave is making its way over the Northern Plains, resulting in mid to high level cloud cover and scattered showers/storms over the western SD plains.

Another embedded wave pushes through the region later today with a sfc low and attendant front developing over western SD. Ahead of the front, a modestly unstable airmass with 1500-2500 J/kg ML CAPE will develop across southern SD. Increasing upper level winds will also support 40-50kt of bulk shear. This will support organized convection and supercells with a large hail and damaging wind threat. CAMs show convection developing east of the Black Hills in the late afternoon and moving eastward. A second line of storms develops over northeastern WY later on in the evening. Showers/storms will continue through the overnight hours, though severe threat should diminish after sunset.

Severe weather is possible again Tuesday afternoon and evening as another wave moves through the area. This threat is a bit more conditional as it will depend on how things evolve overnight tonight and the location of any outflow boundaries. Chances for storms continue into Wednesday.

The upper level pattern shifts later this week as a strong ridge builds over the western US and overspreads the region. Our CWA will sit on the northeastern periphery of the ridge, meaning we'll see warmer temps and continued chances for storms through the end of the week.

AVIATION

(For the 18Z TAFS Through 18Z Wednesday) Issued At 1116 AM MDT Tue Aug 18 2026

Isolated/scattered thunderstorms with gusty, erratic winds will develop after 18/21z, waning by 19/06z. Local IFR conditions will occur with the strongest storms. Outside of storms, VFR conditions will prevail through the period.

UNR WATCHES/WARNINGS/ADVISORIES

SD...None. WY...None.